Rm object literal shorthand -- back down to <0.5kb! #cuttingFeatures

Our own practical uses of Pjs avoid it because:
- for no semantic reason, it looks very syntactically different
- it's just begging for annoyance later when you want super and have to
  go back and change how all the other methods are defined, kinda like
  using 2-line if-statements without braces and later when you want a
  3rd line you have to go back and add braces
- prefixing slot names with a dot . even when defining them makes them
  more greppable

We clearly don't care about this feature, there aren't even any tests
specifically for it. (Many tangentially used passing the shorthand
object literal directly to P, but no tests at all would break if the
returned object literal wasn't merged into the prototype.)

Recommend --word-diff-regex='\w+|.' to view diff.
Don't pass class itself as `this` to definition fn #cuttingFeatures

Undocumented and unnecessary since the class itself is passed in as the
3rd argument, and discouraged in favor of using the 3rd argument because
`this` won't minify.
Don't fail silently if .init isn't a function #cuttingFeatures

Because of the check for inheriting a non-pjs class, the only way for
that to happen is if you monkey-patch .init to something that isn't a
function, in which case you'll get a

    TypeError: Object ${thing you monkey-patched .init to} has no method 'apply'

which I feel like is excellent behavior.

<0.4kb now!
Simplify check if inheriting from a non-Pjs class

If proto.init is truthy but not a function, like 1 or something, you'll
get a

    TypeError: Object 1 has no method 'apply'

which I feel like is excellent behavior.

If we're inheriting from a Pjs class but `proto.init` is overridden to a
falsy value, we'll think we're inheriting from a non-Pjs class and set
`proto.init` to the superclass constructor, which isn't the most
defensive, fail-early thing to do, but is also what happened prior to
this commit.

Really, to be defensive in our non-pjs check, we should check
`('init' in proto)`, so if `proto.init` is overridden to anything
but a function it'll TypeError like above.